Determination of Collar’s Triangle of Forces on a Flexible Wing based on Particle Tracking Velocimetry Measurements

The three components in Collar’s triangle of forces (aerodynamic, elastic and inertial) acting on a flexible wing are determined, based on integrated optical measurements of the structural and the aerodynamic response to steady and unsteady periodic inflow conditions. The measurement device is a coaxial volumetric velocimeter mounted on a robotic arm, which is used to perform optical measurements of fiducial markers on the wing surface and simultaneously of helium-filled soap bubbles that are used as flow tracers. The optical measurements of the structural markers and the flow tracers are both processed with the Lagrangian particle tracking algorithm Shake-The-Box. Subsequently, physical models are used to determine the inertial and the elastic force of the aeroelastic interaction from the marker tracking results, and to determine the unsteady aerodynamic lift force from the flow velocity fields. The results of this integrated aeroelastic characterization approach are in physical agreement with each other according to the equilibrium of forces in Collar’s triangle and good agreement with external reference measurements.